1. Field of the Invention
The present invention relates to a novel process for the production of a cholecystokinin-pancreozymin C-terminal peptide amide sulfate ester of the formula (I) ##STR1## where R.sub.1 represents Asp-- or Asp--Arg--Asp--.
2. Description of the Prior Art
Cholecystokinin-pancreozymin (hereinafter referred to simply as CCK) is a gastrointestinal peptide hormone consisting of 33 amino acid residues, and has the gallbladder contraction and pancreatic secretion effects, thus playing an important role in the digestive and absorption system.
Further, it has been found that such effects of CCK are derived from its C-terminal octapeptide amide sulfate ester and that cholecystokinin-pancreozymin C-terminal octapeptide amide sulfate ester (in the formula (I), R.sub.1 =Asp--) (hereinafter referred to as CCK-8) has a stronger activity than the natural CCK. Thus, various studies have been made to synthesize the CCK-8 and its homologues such as cholecystokinin-pancreozymin C-terminal decapeptide amide sulfate ester (in the formula (I), R.sub.1 =Asp--Arg--Asp--) (hereinafter referred to as CCK-10).
For the production of the compound of the formula (I), there has been known (1) a method wherein free octapeptide amide is reacted with concentrated sulfuric acid or a mixture of sulfuric acid and potassium hydrogensulfate at a lower temperature (U.S. Pat. No. 3,705,140), or (2) a method wherein a protected peptide amide of the formula (II) EQU R.sub.2 -Tyr-Met-Gly-Trp-Met-Asp-Phe-NH.sub.2 (II)
where R.sub.2 is ##STR2## wherein X is an amino protecting group and Y is absence or a carboxyl protecting group, is reacted with sulfur trioxide-pyridine complex to form a sulfate ester and then the protecting groups are removed [J.Am.Chem.Soc. 92, 195 to 199 (1970)].
In these methods, the sulfate esterified reaction solution is poured into a cold ethanol for precipitation and the precipitates are dissolved in an ammonium carbonate solution and refined by means of e.g. DEAE-Sephadex thereby to obtain the intended product. However, the compound of the formula (I) is extremely unstable, and the decomposition is likely to occur during the post-treatment, which leads to reduction of yield and activity. The yield is 10% according to the method (1) and 30% according to the method (2), thus presenting extremely low yield in either case.